[mutter/wip/carlosg/clip-me-harder: 5/5] compositor: Clip obscured background areas

[Carlos Garnacho <carlosg src gnome org>]

commit 53eca1c49f08f4b53d8f163ffb82fe75db695b58
Author: Carlos Garnacho <carlosg gnome org>
Date:   Sun Jan 27 15:49:41 2019 +0100

    compositor: Clip obscured background areas
    
    The MetaBackgroundActor was ignoring the unobscured area altogether,
    and just painted according to the clip area. Check the unobscured
    area too, as it might well be covered by client windows.
    
    https://gitlab.gnome.org/GNOME/mutter/merge_requests/698

 src/compositor/meta-background-actor.c | 64 +++++++++++++++++++++++++---------
 1 file changed, 48 insertions(+), 16 deletions(-)
---
diff --git a/src/compositor/meta-background-actor.c b/src/compositor/meta-background-actor.c
index 7c0f82d1a..48f745b38 100644
--- a/src/compositor/meta-background-actor.c
+++ b/src/compositor/meta-background-actor.c
@@ -179,6 +179,7 @@ struct _MetaBackgroundActor
   gboolean force_bilinear;
 
   cairo_region_t *clip_region;
+  cairo_region_t *unobscured_region;
 };
 
 static void cullable_iface_init (MetaCullableInterface *iface);
@@ -195,12 +196,22 @@ set_clip_region (MetaBackgroundActor *self,
     self->clip_region = cairo_region_copy (clip_region);
 }
 
+static void
+set_unobscured_region (MetaBackgroundActor *self,
+                       cairo_region_t      *unobscured_region)
+{
+  g_clear_pointer (&self->unobscured_region, cairo_region_destroy);
+  if (unobscured_region)
+    self->unobscured_region = cairo_region_copy (unobscured_region);
+}
+
 static void
 meta_background_actor_dispose (GObject *object)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (object);
 
   set_clip_region (self, NULL);
+  set_unobscured_region (self, NULL);
   meta_background_actor_set_background (self, NULL);
   if (self->pipeline)
     {
@@ -502,7 +513,8 @@ meta_background_actor_paint (ClutterActor *actor)
   ClutterActorBox actor_box;
   cairo_rectangle_int_t actor_pixel_rect;
   CoglFramebuffer *fb;
-  int i;
+  cairo_region_t *region;
+  int i, n_rects;
 
   if ((self->clip_region && cairo_region_is_empty (self->clip_region)))
     return;
@@ -524,27 +536,43 @@ meta_background_actor_paint (ClutterActor *actor)
 
   /* Now figure out what to actually paint.
    */
-  if (self->clip_region != NULL)
+  if (self->clip_region)
     {
-      int n_rects = cairo_region_num_rectangles (self->clip_region);
-      if (n_rects <= MAX_RECTS)
-        {
-           for (i = 0; i < n_rects; i++)
-             {
-               cairo_rectangle_int_t rect;
-               cairo_region_get_rectangle (self->clip_region, i, &rect);
+      region = cairo_region_copy (self->clip_region);
+      cairo_region_intersect_rectangle (region, &actor_pixel_rect);
+    }
+  else
+    {
+      region = cairo_region_create_rectangle (&actor_pixel_rect);
+    }
 
-               if (!gdk_rectangle_intersect (&actor_pixel_rect, &rect, &rect))
-                 continue;
+  if (self->unobscured_region)
+    cairo_region_intersect (region, self->unobscured_region);
 
-               paint_clipped_rectangle (fb, self->pipeline, &rect, &self->texture_area);
-             }
+  if (cairo_region_is_empty (region))
+    {
+      cairo_region_destroy (region);
+      return;
+    }
 
-           return;
+  n_rects = cairo_region_num_rectangles (region);
+  if (n_rects <= MAX_RECTS)
+    {
+      for (i = 0; i < n_rects; i++)
+        {
+          cairo_rectangle_int_t rect;
+          cairo_region_get_rectangle (region, i, &rect);
+          paint_clipped_rectangle (fb, self->pipeline, &rect,
+                                   &self->texture_area);
         }
     }
-
-  paint_clipped_rectangle (fb, self->pipeline, &actor_pixel_rect, &self->texture_area);
+  else
+    {
+      cairo_rectangle_int_t rect;
+      cairo_region_get_extents (region, &rect);
+      paint_clipped_rectangle (fb, self->pipeline, &rect,
+                               &self->texture_area);
+    }
 }
 
 static void
@@ -798,6 +826,8 @@ meta_background_actor_cull_out (MetaCullable   *cullable,
                                 cairo_region_t *clip_region)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (cullable);
+
+  set_unobscured_region (self, unobscured_region);
   set_clip_region (self, clip_region);
 }
 
@@ -805,6 +835,8 @@ static void
 meta_background_actor_reset_culling (MetaCullable *cullable)
 {
   MetaBackgroundActor *self = META_BACKGROUND_ACTOR (cullable);
+
+  set_unobscured_region (self, NULL);
   set_clip_region (self, NULL);
 }